1. Field of the Invention
This invention relates to electrical switching apparatus and, more particularly, to circuit breakers, such as a molded case circuit breaker having a barrier for avoiding electrical breakdown due to ionized gases exhausting from an arc extinguishing chamber.
2. Background Information
Electrical switching apparatus include, for example, circuit switching devices and circuit interrupters, such as circuit breakers, network protectors, disconnects, transfer switches, and motor circuit protectors.
Circuit breakers are generally old and well known in the art. Examples of circuit breakers are disclosed in U.S. Pat. Nos. 4,620,076; 4,638,277; 4,650,940; 5,493,092; and 5,753,877.
When the circuit breaker""s separable contacts are opened, an arc is usually created which is accompanied by the generation of ionized gases. This is particularly true for circuit breakers of small physical size with high interrupting ratings. The ionized gases are conductive. Hence, if such gases collect in the vicinity of the line terminals of the circuit breaker, they may cause a phase-to-phase electrical failure between the circuit breaker terminals, and/or a phase-to-ground electrical failure with any metallic enclosure within which the circuit breaker is mounted. This can lead to electrical faults on the line side of the circuit breaker and damage to switchgear equipment.
Circuit breakers typically include vents to allow the ionized gases to quickly escape therefrom. Where wiring terminals are in close proximity to the circuit breaker vents, the problem of electrical faults is especially acute. Accordingly, there is a need for preventing these kinds of electrical breakdowns.
U.S. Pat. No. 4,650,940 discloses a circuit breaker having a flap or barrier, which is disposed within a terminal compartment and over the inner side of an opening for a screwdriver. The ionized gases flowing into the terminal compartment are stopped from flowing through the opening by the flap extending thereacross. The flap is preferably composed of a sheet of fiber or fiber type material, which is chemically and electrically impervious to hot ionized gases. The fiber sheet is folded into a configuration including a central wall portion, an upper foldable flap portion and a lower T-shaped portion. The central wall portion and the lower T-shaped portion are adapted to fit snugly against a compartment wall and an opening from the circuit breaker arc chute. A suitable adhesive is provided between the wall surfaces and the corresponding central wall portion and lower T-shaped portion to retain the folded sheet in place. However, because the fiber sheet is not coupled to the wall or to the terminal collar assembly, it can easily be accidentally removed, thereby allowing a path for ionized gases to reach ground through the screwdriver opening.
Accordingly, there is room for improvement in circuit breakers employing terminal barriers.
These needs and others are satisfied by the invention, which is directed to an electrical switching apparatus, such as a circuit breaker, including a baffle member for arc gases. The baffle member includes a base portion, a flap and a pair of leg members, with the flap extending over a terminal aperture and being deflectable by a tool inserted through the aperture for adjustment of the terminal. The leg members engage terminal compartment side walls and support the baffle member within the terminal compartment.
As one aspect of the invention, an electrical switching apparatus for automatically interrupting an overload current comprises: an electrically insulating housing; an arc chamber within the housing; line and load terminals; separable contacts in series with the line and load terminals; an operating mechanism for moving the separable contacts between an open position and a closed position, the open position of the contacts causing arcing therebetween and the development of ionized gases; the housing including a plurality of walls forming a compartment for containing one of the terminals, with a first wall having an aperture for accessing the one of the terminals and a second wall having an opening between the chamber and the compartment, and a baffle member comprising a base portion, a flap and a pair of leg members, the flap extending over the aperture and being deflectable by a tool inserted through the aperture for adjustment of the one of the terminals, the leg members engaging some of the walls of the compartment, thereby supporting the baffle member within the compartment.
Preferably, the compartment includes a member having protruding portions and each of the leg members has a cut out portion which mates with a corresponding one of the protruding portions.
The baffle member may be a flat member which is folded three times to form the flap and the pair of leg members, with the flap and the leg members each being folded with respect to the base portion.
As another aspect of the invention, a circuit breaker comprises: an electrically insulating housing; line and load terminals; separable contacts within the housing and electrically connected between the line and load terminals; an arc chamber within the housing; and an operating mechanism adapted to move the separable contacts between open and closed positions within the chamber, the housing including a first wall, an opposite second wall, a pair of side walls, and a barrier wall forming a compartment for containing one of the terminals, the barrier wall having an opening between the chamber and the compartment, the first wall having an aperture for accessing the one of the terminals; and a folded baffle member comprising a base portion, a flap and a pair of leg members, the flap extending over the aperture to prevent arc gases from flowing through the aperture and thereby avoiding a phase-to-ground electrical breakdown between the one of the terminals and an electrical conductor adjacent to the aperture, the flap being deflectable by a tool inserted through the aperture for adjustment of the one of the terminals, the leg members engaging the pair of side walls, thereby supporting the baffle member within the compartment.